1. Field of the Invention:
The present invention relates to a method of and an apparatus for thermally recording an image or the like on a thermosensitive recording medium by applying a laser beam or the like to the thermosensitive recording medium.
2. Description of the Related Art:
Thermosensitive recording apparatus for applying thermal energy to a thermosensitive recording medium to record an image or other information thereon are in wide use. Particularly, thermosensitive recording apparatus which employ a laser as a thermal energy source for high-speed recording are known from Japanese laid-open patent publications Nos. 50-23617, 58-94494, 62-77983, and 62-78964, for example.
The applicant has developed a thermosensitive recording medium capable of recording a high-quality image for use in such thermosensitive recording apparatus. The thermosensitive recording medium comprises a support coated with a coloring agent, a color developer, and light-absorbing dyes, and produces a color whose density depends on the thermal energy that is applied to the thermosensitive recording medium. For details, reference should be made to Japanese laid-open patent publications Nos. 5-301447 and 5-24219.
The thermosensitive recording medium has a thermosensitive layer on the support. The thermosensitive layer is produced by coating a coating solution on the support. The coating solution contains an emulsion which is prepared by dissolving microcapsules containing at least a basic dye precursor, a color developer, and light-absorbing dyes into an organic solvent that is either slightly water-soluble or water-insoluble, and then emulsifying and dispersing the dissolved materials.
The thermosensitive recording medium produces no color with low thermal energy applied, so that it can be held stably in storage. To bring the thermosensitive recording medium into a desired colored condition, therefore, it is necessary to apply a considerable amount of thermal energy to the thermosensitive recording medium. As a result, the dynamic range of a recorded image is narrowed by a value corresponding to the threshold level of the thermal energy which is applied until the thermosensitive recording medium is colored, making it difficult to obtain a high-gradation image. In addition, the thermosensitive recording apparatus which causes the thermosensitive recording medium to be colored is subjected to a considerable burden.
The applicant has also proposed a thermosensitive recording apparatus for preheating a thermosensitive recording medium up to a certain temperature below a coloring temperature and thereafter applying a laser beam to the thermosensitive recording medium to produce a color thereon, as disclosed in Japanese patent application No. 5-38888. The proposed thermosensitive recording apparatus can produce a high-gradation image easily and highly accurately, and allows the burden on the heating means to be reduced.
It is known that the density of an image which is recorded on a thermosensitive recording medium by applying a predetermined amount of thermal energy thereto increases with time when held in storage at normal temperature. Therefore, images recorded on a thermosensitive recording medium have different densities immediately after they are recorded and upon elapse of a certain period of time after they are recorded. In view of such a drawback, the applicant has proposed a method of and an apparatus for thermally recording an image by applying a laser beam to a thermosensitive recording medium to record a visible image thereon and thereafter heating the thermosensitive recording medium again to a temperature lower than a coloring temperature, as disclosed in Japanese patent application No. 5-205965. The disclosed process accelerates a coloring reaction immediately after the image has been recorded, thereby producing an image of stable density.
However, the disclosed process is disadvantageous for the reasons given below. Since the thermosensitive recording medium is normally biaxially oriented, when the thermosensitive recording medium is heated to a temperature lower than a coloring temperature before and/or after an image is recorded, the thermosensitive recording medium is apt to shrink. When the thermosensitive recording medium is shrunk, the image recorded thereon is reduced in size. As a consequence, a desired image cannot be obtained on the thermosensitive recording medium.